New metal alloy material and method of heat treating



United States Patent Ofiice 3,063,833 Patented Nov. 13, 1962 3,063,833NEW METAL ALLOY MATERIAL AND METHOD OF HEAT TREATING Beniamin F.Shepherd, Phillipsburg, N.J., assignor t Ingersoll-Rand Company, NewYork, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 14, 1959,Ser. No. 859,162 2 Claims. (Cl. 75-159) This invention relates to a newmetal alloy material and to a method of heat treating the material toincrease its physical properties.

The investigation leading to the discovery of this new metal wasprompted by the need for a metal which is highly resistant to corrosionand in which castings of the material are capable of withstanding highpressure and are hydrostatically sound. Specifically, the investigationrelated to the production of a metal which could be used in a highpressure pump for use in pumping salt water or a similar corrosiveliquid.

It is known that a 70/30 copper-nickel alloy has the necessarycharacteristic of resisting corrosion, however it has relatively lowphysical characteristics which makes it unsatisfactory for the purposementioned. It is also known that the addition of silicon to thiscupro-nickel will increase its physical characteristics, for example, acopper-nickel alloy containing about .5% silicon and .7% iron, about25,000 p.s.i. yield strength is obtainable with a tensile strength ofapproximately 55,000 p.s.i. Unfortunately, however, the addition of thisamount of silicon very seriously afiects the weldability of thematerial. This is an extreme disadvantage in using the material in, forexample, pump casings.

In an effort to overcome this disadvantage and to increase the physicalcharacteristics of a basically coppernickel alloy containing 70% copperand 30% nickel, it was found that the addition of columbium and siliconresulted in a new material having a dramatic increase in the physicalproperties and which is weldable even with relatively high siliconcontent.

The first experiment was conducted using a 70/30 copper-nickel alloycontaining columbium in the range of 33% to .83%; manganese within therange of .83% to 1.41% and iron in the range of 50% to 1.07%. It ispreferable that the manganese percentage be about twice that of siliconat the lower levels, and the iron percentage around .3% to providecorrosion resistance. Insofar as this invention is concerned it isbelieved that the specific percentage of the manganese and iron contentis relatively unimportant and do not in any way affect the resultsobtained by the addition of various quantities of silicon and columbium.It is merely desirable that these two elements be present and inpercentages within the stated ranges. Further reference to theseelements namely, iron and manganese, 'will be omitted although it is tobe understood that these two elements in approximately this proportionwere present in all the tests conducted.

In this particular test, the percentage of silicon was varied over arange of from .25% to .69%. The tensile strength of the material, ascompared to a material of similar composition except for columbium, wasincreased approximately 15,000 p.s.i. at the lower silicon level andapproximately 27,000 p.s.i. at the upper level. More particularly, thealloy with 25% silicon, but without columbium, has a tensile strength ofabout 47,000 p.s.i. and with .69% silicon the tensile strength is about68,000 p.s.i., whereas when columbium was added in the quantitiesstated, the tensile strength at .25 silicon content Was increased toapproximately 62,000 p.s.i. whereas at the silicon level of .69% thetensile strength was found to be in the neighborhood of 95,000 p.s.i.

Similar gains were also made in the yield strength. At the .25 siliconlevel, the yield strength was increased from about 18,000 p.s.i. toabout 26,000 p.s.i. and at the .69% silicon level the yield strength wasraised from about 42,000 p.s.i. to approximately 68,000 p.s.i. by theaddition of columbium.

Another point of considerable interest that was noted as a consequenceof these comparative tests was that the alloy containing silicon, but nocolumbium, and the alloy containing both silicon and columbium had aboutthe same percent of elongation or hardness for a given yield and tensilestrength.

Subsequent to this test, additional experiments were conducted in whichthe amount of columbium for the percentage of silicon was varied overthe silicon range to determine the effect of columbium on the increasedphysical characteristics and weldability of the new material. In thisparticular test, the combined percentage of silicon and columbium wasvaried over the range of from .6% to 1.5%. It was concluded thatalthough there seemed to be a rather broad range of relationship betweenthe comparative percentages of silicon to columbium over the rangeinvestigated, it was found that the addition of columbium at the lowersilicon level very greatly increased the effectiveness of silicon inincreasing the physical properties of the material. This was noted to betrue particularly below silicon levels of about .3%. On the other hand,at the silicon levels above 3% it was found desirable to have thecolumbium at least equal to and preferably greater than the percentagesof silicon. It is believed that this excess of columbium is necessaryprimarily in order to obtain weldability of the material; the excess ofcolumbium over silicon would not be required at this higher siliconlevel, however, if it is not necessary or desirable to make the materialweldable.

It was further noted that when the silicon content was increased above.8%, the hardness of the material was correspondingly greatly increasedand the percentage of elongation was reduced to something less than 10%.This is believed to be generally undesirable and it was accordinglyconcluded that the silicon content should be not greater than about .8%due to the loss of ductility, and the combined percentage of columbiumand silicon should not exceed about 1.75% and in which the columbiumwould be equal to or greater than the silicon percentage whenever thesilicon percentage was greater than about 3%.

It was discovered further that the mechanical properties of this alloy,containing columbium and silicon in the percentages and ratiosheretofore discussed, can be increased by controlling the cooling rateof the alloy. Accompanying the increase in yield and tensile strength,there was a corresponding change in the percent of elon gation. That is,the percent of elongation remained about the same for given yield andtensile strengths regardless of the cooling rate.

In the first test, several test bars were knocked out of their moldsabout twenty minutes after the bars were poured and, at which time, thebar temperatures were approximately 1400 F. A second group of bars waspermitted to cool for approximately two hours in the molds. Thetemperature of the bars of the second group was 500 F. at the time ofknocking the bars free of the molds. The slowly cooled bars hadapproximately 10% higher yield strength and approximately 5% highertensile strength than the more quickly cooled bar.

Following this test, an additional experiment was performed in which thecast bars were subjected to what I call homogenization heat treatment.This comprised reheating the cast bars up to a temperature of within therange of 900 F. to 1550 F. and holding at that temperature for a periodof time and then cooling either rapidly, as by air cooling, or slowly byfurnace cooling for a period of about eight to ten hours. It was learnedthat heating the casting to a temperature within said range for a periodof one hour followed by air cooling, resulted in no observable change inthe strength of the material. However, when the temperature was held ata value Within said temperature range for a period of one hour andallowed to cool slowly in a laboratory furnace overnight down to atemperature of approximately 500 F., a very significant increase inyield and tensile strength was obtained. For example, several tests wereconducted using test bars containing various percentages of siliconvarying from 25% to .65% in which the bars were heated to 1200 F. andheld at this temperature for a period of one hour and then permitted tocool in the furnace down to a temperature of about 500 F. There was anincrease of tensile strength of between 1l,000 psi. and 7,000 psi. ascompared to the same bars when knocked out of the mold two hours afterpouring and permitted to air cool.

Other tests were conducted in which the casting was held at atemperature of 900 F. for a period of twentyfour hours and thereafterair cooled. This, also, resulted in a significant increase in thephysical characteristics of the casting. This indicates that thehomogenizing treatment to increase the yield and tensile strength of thematerial may be obtained either by heating for a relatively shortperiod-e.g., approximately one hour, at a temperature within the rangeof 900 to 1550 F. and thereafter cooling slowly over a relatively longperiode.g., around six to ten hours; or reheating to a temperaturewithin such range and holding it at that temperature a relatively longperiod-cg, six to ten hours, and then cooling more rapidly. In eithercase, it is believed necessary to hold the temperature of the alloy atan elevated value for a sufficiently long period to permit thehomogenizing process to condition the material for the cooling process.

It is generally believed that when heretofore known metals are subjectedto normal foundry practice to form castings, the more rapidly cooledsections of the casting have higher mechanical properties than the moreslowly cooled sections. Thus, thin sections are generally credited withsuperior mechanical properties to the heavier sections, which cool moreslowly. It is evident from the foregoing that in this particular alloythe thin sections will have lower mechanical properties due to morerapid cooling. The homogenizing treatment will cancel the variations incooling rates and enable the maximum strength potential to be realizedin both thick and thin sections of the same casting.

I claim:

1. A cupro-nickel alloy comprising copper within the range of about 66%to about 70%, manganese within the range of about .83% to about 1.41%,iron in the range of about to about 1.07%, silicon and at least onemetal of the group consisting of tantalum and columbiurn the combinedpercentages of which do not exceed 1.75% and in which the percentage ofthe metal in said group consisting of tantalum and columbium is equal toor greater than the percentage of silicon when the silicon percentageexceeds 3%, and the balance nickel.

2. A cupro-nickel alloy comprising copper Within the range of about 66%to about 70%, manganese within the range of about .83% to about 1.41%,iron in the range of about 50% to about 1.07%, silicon in an amount notexceeding .8% and at least one metal of the group consisting of tantalumand columbium in a percentage equal to or greater than the siliconpercent 'When the silicon percent is greater than or equal to .3% andthe balance nickel.

References Cited in the tile of this patent UNITED STATES PATENTS

1. A CUPRO-NICKEL ALLOY COMPRISING COPPER WITHIN THE RANGE OF ABOUT 66%TO ABOUT 70%, MANGANESE WITHINN THE RANGE OF ABOUT .83% TO ABOUT 1.41%,IRON IN THE RANGE OF ABOUT .50% TO ABOUT 1.07%, SILICON AND AT LEAST ONEMETAL OF THE GROUP CONSISTING OF TANTALUM AND COLUM-MBIUM THE COMBINEDPERCENTAGES OF WHICH DO NOT EXCEED 1.75% AND IN WHICH THE PERCENTAGE OFTHE METAL IN SAIDD GROUP CONSISTING OF TANTALUM AND COLUMBIUM IS EQUALTO OR GREATER THAN THE PERCENTAGE OF SILICON WHEN THE SILICON PERCENTAGEEXCEEDS .3%, AND THE BALANCE NICKEL..